To a driving force transmission shaft, such as a drive shaft and a propeller shaft, of rotating shafts of an automobile, undesirable vibrations occur as the driving force transmission shaft rotates. In addition to bending vibrations and torsional vibrations caused by a rotation of the driving force transmission shaft itself, external factors cause other kinds of vibrations. In order to uniformly suppress the vibrations caused by these various factors, a damper device, which is a dynamic vibration absorber (also referred to as “dynamic damper”), having a weight (mass body) is attached to the driving force transmission shaft.
In some of the conventional damper devices, the vibration damping performance deteriorates when the rotating shaft rotates at rotational speeds other than a specific rotational speed at which a vibration is suppressed. In order to avoid this, a weight attached to some damper devises is formed so as to be movable in the diameter direction. For example, in Patent Document 1, an inertial body, which is a weight composed of a plurality of members, is arranged annularly around the driving force transmission shaft. Rubber elastic bodies are arranged annularly around a plurality of the inertial bodies. And, the inertial bodies are configured to be movable in the diameter direction. Also, in Patent Document 2, the inertial body is configured to be movable in the diameter direction by arranging a weight member, which is a weight composed of a plurality of members, annularly around a driving force transmission shaft, and enclosing compressible fluid adjacent to the radially outside of a plurality of the weight members.
However, the rubber members and fluids remarkably change in characteristics according to environmental changes such as temperature changes. Then, the performance of the rubber member and fluids to move the weight in the diameter direction also varies according to environmental changes. Therefore, there was a problem that the weight cannot stably move in the diameter direction depending on the environments.